# Isaac Newton’s Principia and Life after It

Philosophiae Naturalis Principia Mathematica was Newton’s historic achievement. It altered the course of science from that day to this. In summer 1684, Newton began this work, partially stimulated by a visit from the British astronomer Edmond Halley. Halley, too, had been pondering the problem of orbital dynamics. What he discovered during his visit was that Newton had solved the problem but discussed it with no one for two decades because he knew his mathematics was slightly off.
Newton did send his demonstration—Halley had made him promise—but took three months to do so. The short tract (pamphlet) On Motion was already being improved by Newton during those three months. Two-and-a-half years more of work enlarged and improved the tract to become Principia (Newton wrote his works in Latin).
Newton’s earlier On Motion had not stated the law of universal gravitation nor the three Newtonian laws of motion. It had been a treatise on planetary dynamics. Only during his thirty months of revising it did Newton advance the principle of inertia (the first law), his precise quantitative statement of the action of the forces between bodies (the second law), and the principle that for every action there is an opposite and equal reaction (the third law).
Note that these three laws of the mechanics of relationships among visible entities must not be confused with Newton’s mechanics, a later attempt to explain phenomena by reference to imagined mechanisms among invisible particles of matter.
“Analysis of circular motion in terms of these . . . [three] laws yielded a formula of the quantitative measure, in terms of a body’s velocity and mass, of the centripetal force necessary to divert a body from its rectilinear path into a given circle.”
Applying this to the planets in their orbits around the sun, to the satellites of Jupiter, and to the earth and its moon, Newton concluded that the same force, governed by a single quantitative law, operated for all three phenomena. He applied to it the ancient Latin word gravitas. The law of universal gravitation, confirmed by his observation of tides and the orbits of comets, asserts that every particle of matter in the universe (existence) attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
In 1686, Newton reported his achievement to the Royal Society, sending the complete manuscript of Book One. His old nemesis, Hooke, immediately again cried “plagiarism.” The charge is not now viewed as true in any meaningful sense. But Hooke, sickly and in decline, longed to be acknowledged in Newton’s book.
Instead, Newton went through his manuscript eliminating virtually any reference to Hooke or his work. Furious, he refused to publish Opticks as planned. He would not accept the presidency of the Royal Society until Hooke died. He lamented: “I can calculate the motion of heavenly bodies, but not the madness of people.
Not having published Opticks mattered to Newton, who craved reassurance of the value of his work, but, in the end, it did not matter to the world; it was Principia that propelled Newton to international stature. During his life, scientists on the Continent did resist the notion of action at a distance but still praised Newton’s sheer expertise. Young scientists in England and Scotland embraced him utterly, almost immediately. It is said that within a generation virtually all salaried positions for a scientist in England, including chairs at Oxford and Cambridge, were held by “Newtonians.” The admiration gave Newton a certain peace as he became the recognized patron of a circle of brilliant young scientists. His friendship with one, Nicolas Fatio de Duillier, a Swiss-born mathematician, reportedly became the most profound experience of Newton’s adulthood.
Crowning the Age of Science, Principia (and all Newton’s other published works that it launched into prominence), like a magnet aligning iron filings, seemed to turn virtually every intellect—first in Europe, then abroad—toward one emblazoned message: Nature, on earth and in the heavens, is a lawful system, understandable by man’s reason, without the need for divine revelation, only observation and reason guided by scientific methods. For many, the message went on: Nature and man’s place in it are a book in which we read of God’s creation and his intention that humankind understand it and through understanding benefit—and know God’s plan for human morality and society and, thereby, God’s goodness.
That might well be a valedictory pronouncement on the Age of Science and the theme of the Age of Enlightenment yet to begin. The confidence, excitement, and sometimes hubris of the Age of Enlightenment cannot be understood without grasping the impact of Newton’s achievements.
If man’s mind could discern the exact mathematics of the orbiting planets and their satellites, the laws governing the earth and the heavens—and, for good measure, the tides, the physics of color, and the exacting mathematics of the infinitesimal calculus—then what possibly could limit the reach of his mind and its dominion over nature?
With many thanks to Newton, the Enlightenment, which characterized the next (eighteenth) century, began with an inexhaustible bank account of confidence. That intellectual exuberance was built throughout a century that saw the Industrial Revolution, the political revolutions (in America and France), and the Romantic revolution (the latter often mistaken for an “anti-Enlightenment” movement but was in fact an application of Enlightenment principles—essentially the principle of free will—to human creation and response to art). Newton’s full impact, however, must be the subject of another blog.
What did Newton, riding this flood tide of fame and influence, do next? He had no apparent doubt about God’s existence as creator of an orderly, lawful universe that could not have resulted from blind chance. He wrote: “I have a fundamental belief in the Bible as the Word of God, written by those who were inspired. I study the Bible daily.” Whether or not he studied the Bible daily, it was unsurprising for a scientist of his time to believe in God. Indeed, Newton’s work hugely strengthened belief in God as creator of the lawful universe and launched a century of faith resting upon deistic belief in the “Divine Architect.” Until the work of Charles Darwin on evolution, in 1859, this “argument from design” seemed irrefutable.
Newton took pains to declare his faith, offering such aphorisms as “In the absence of any other proof, the thumb alone would convince me of God’s existence.
A fervent, if “free-thinking,” Calvinist, he lent his reputation to resisting the attempt by James II to make Cambridge Catholic. He was elected to represent the university at the convention that settled the issue. This drew Newton out of his seclusion; he met John Locke and other contemporary intellectuals.
Newton, after a cloistered life in academia, and years of solitary creative work, fell in love with the excitement of life in London. He never returned to academia or did much additional scientific work. He sought a place “in the world” through a new friend, Lord Halifax, and, in 1696, became warden of the mint. Without immediately severing his Cambridge connections, he moved to London and made his life there.
Then, tragedy struck. Newton’s great friend Fatio de Duillier fell ill and prepared to return to his family in Switzerland. A terrible distress seized Newton. He offered every support to his friend, but for reasons not known their correspondence broke off. Newton, as though crazed with frustration, inexplicably turned to savagely attack two personal friends, Samuel Pepys and John Locke, breaking off relations with the first and accusing the second of trying to pimp for him. Both friends became alarmed for Newton’s sanity, and, indeed, this is when he suffered the second nervous breakdown mentioned above.
Newton always recovered, but only briefly engaged in additional scientific work. When he moved to London, he seemed to move away from his work in science. His income as warden, later master, of the mint made him a rich man. The position, frankly, was viewed as a sinecure, a handsome reward for political loyalty. But a sinecure was not for Isaac Newton. The great recoinage required his diligence, and from then on he actively exercised his authority. He hounded counterfeiters in London, sending not a few to the gallows, and did so with the rage that had been part of his personality since childhood.
In these years, he turned to investigating religion, sharing his ideas with Locke (who came to forgive his attacks). His studies were interpretations of biblical prophecies and ancient chronology. His works on these, however, were published only after his death.
Again, Newton’s impact on English and then European science, and beyond, must await another blog. But he became the godfather of English science, was sought out by the French Academy, knighted by Queen Anne in 1705, and, in effect, ruled the Royal Society. He used his position there to have his way with scientists and would brook no opposition or objections. When crossed, he was vengeful.
He thus was drawn into a legendary fray that continued for years when Leibniz advanced claims to have been the first to create the calculus. Reportedly, Newton could not edit a paper on any topic without inserting a paragraph or two of furious attacks on Leibniz. Close historical examination confirms that the two men developed calculus entirely independently.
In his final years, Newton oversaw new editions of his works, editions in Latin and English. Into some editions of Principia, he introduced new material. Professional editors, too, made alterations in bringing out other editions.
Newton’s life narrowed to presiding at meetings of the Society, albeit often dozing, and continuing to supervise the mint. He lived almost until his death with his niece, Catherine Barton Conduitt, and her husband.
In the end, perhaps, the world granted all the personal recognition that since boyhood he felt he had been denied. At age eighty-four, in 1727, Sir Isaac Newton died in his sleep and was buried with pomp and ceremony in Westminster Abbey, London. His epitaph broadcasts the spin on his work that the church demanded: “Diligent, sagacious and faithful, in his expositions of nature, antiquity and the Holy Scriptures, he vindicated by his philosophy the majesty of God mighty and good and expressed the simplicity of the gospel in his manners.”
In one of the most famous “epitaphs” in history, although not one carved in stone, Alexander Pope wrote: “Nature and nature’s laws lay hid in night; God said, ‘Let Newton be’ and all was light." This “spin” on Newton’s achievements, one Newton himself asserted, would become a first premise of the Age of Enlightenment. In nature, we read God’s intentions for human society, for morality, for worship.
But the deists used logical consistency, a prime value of the Age of Enlightenment, to snatch Newton’s message away from religions of the gospels. God is the architect, the workman, who fashioned the universe. We know nothing of Him but from the evidence of His handiwork. Revelation, the gospels, miracles, the content of the Bible itself cannot be confirmed by observation of nature. Nature gives no evidence of heaven or hell. Infer God as Newton inferred the laws governing existence. Study nature to know the divine intent for humankind. No other source warrants our attention.
It is fair to say, I think, that the eighteenth-century Age of Enlightenment, following the seventeenth- century Scientific Revolution, devoted itself to deriving every implication of that view for the whole of mankind’s quest for knowledge.
The creation is the Bible of the Deist. He there reads, in the handwriting of the Creator himself, the certainty of His existence and the immutability of His power, and all other Bibles and Testaments are to him forgeries.
Thomas Paine

The question before the human race is, whether the God of nature shall govern the world by his own laws, or whether priests and kings shall rule it by fictitious miracles?